“Superhydrophobic surfaces” are not scientifically defined; however, superhydrophobic surfaces generally refer to surfaces that have a water contact angle of 150° or more and are hardly wetted with water. It is generally known that a solid surface formed from a low-surface-energy substance comprising fluorine, etc., as a main component can have excellent hydrophobicity. It is also known that the hydrophobicity is further increased by imparting appropriate roughness to the surface.
Meanwhile, compounds having pores in a solid structure are called porous compounds. Various porous materials, such as organic substances and inorganic substances, are known. Typical examples thereof include zeolite, activated carbon, silica gel, molecular sieves, and the like. Porous coordination polymers (PCPs) have recently attracted attention as new porous materials. Porous coordination polymers are materials that form porous structures by taking advantage of the coordinate bonds between metal ions and organic ligands. They are expected to find application in gas storage or separation, catalysts, etc. However, many porous coordination polymers reported to date have limited practical applicability due to their low stability in water and propensity for degradation upon exposure to water.
Accordingly, in order to improve the stability of porous coordination polymers in water, attempts have been made to impart (super) hydrophobicity to the surface of porous coordination polymers. NPL 1 teaches that PCP comprising a fluorinated aromatic ring as an organic ligand achieves a contact angle of 151±1°. NPL 2 and NPL 3 teach that PCP comprising a compound terminated with bulky alkyl chains as an organic ligand achieves a contact angle of more than 150°.